If you believe in a local flood then how do you make sense that God promised never to do it again:

11 And I will establish my covenant with you, neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth.12 And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations:13 I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.14 And it shall come to pass, when I bring a cloud over the earth, that the bow shall be seen in the cloud:15 And I will remember my covenant, which is between me and you and every living creature of all flesh; and the waters shall no more become a flood to destroy all flesh.16 And the bow shall be in the cloud; and I will look upon it, that I may remember the everlasting covenant between God and every living creature of all flesh that is upon the earth.

and how do you reconcile "neither shall all flesh be cut off any more by the waters of a flood". The way I see it, all flesh was subject to a flood in that day. It had been spread out after the attempt to build the tower of babel.

If you believe in a local flood then how do you make sense that God promised never to do it again:

11 And I will establish my covenant with you, neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth.12 And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations:13 I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.14 And it shall come to pass, when I bring a cloud over the earth, that the bow shall be seen in the cloud:15 And I will remember my covenant, which is between me and you and every living creature of all flesh; and the waters shall no more become a flood to destroy all flesh.16 And the bow shall be in the cloud; and I will look upon it, that I may remember the everlasting covenant between God and every living creature of all flesh that is upon the earth.

and how do you reconcile "neither shall all flesh be cut off any more by the waters of a flood". The way I see it, all flesh was subject to a flood in that day. It had been spread out after the attempt to build the tower of babel.

That's an excellent point. If the Lord promised to never send a 'local flood' again then He has violated that promise countless times and every rainbow would serve as a sign that He broke that promise. But we know that " God is not a man, that he should lie" and He has lived up to His word, not only about the universal flood but about everything else He says in His word. Not only so, but the evidence for the world-wide flood is (putting it mildly) massive.

And if it was local, why did Noah have to build an ark? He could have just migrated to another part of the earth.

I stated these arguments on Christian Forums months ago against some well-versed theistic evolutionists, but the conclusions they came to amounted to an unbelievable stretching of logic and/or a deliberate mental manipulation of scripture. The plain spoken Word is never good enough for them and Moses always takes a back-seat to Darwin.